The present invention relates generally to a zoom lens and an imaging apparatus incorporating the same, and more particularly to a zoom lens of small format that lends itself to imaging apparatus inclusive of video cameras and digital cameras.
In recent years, imaging apparatus such as digital cameras designed to take images of subjects using solid-state imaging devices such as CCDs or CMOSs have became mainstream in place of silver-halide film cameras. Further, they have now a wide spectrum of categories from the commercial high-end type to the compact low-end type.
The present invention gives weight to the compact low-end type category in particular. Users of such low-end type digital cameras would enjoy snapping shots over a wide range of scenes at anytime in anyplace. For this reason, preference is given to small-format digital cameras, especially of the type that can be well put away in the pockets of clothing or baggage, is convenient to carry around, and is slimmed down in their thickness direction, and there is a mounting demand for size reductions of taking lens systems, too.
On the other hand, as the pixels of imaging devices are now on the increase, there is an increasing demand for higher optical performance keeping pace with a lot more pixels. Further, to make sure mass productivity, it is required to minimize the sensitivity of optical performance deterioration to production errors in the process, of processing and assembling lenses. From the point of view of making taking ranges wide, high zooming lenses having zoom ratios exceeding 5 or 7, too, are generally available; much higher zoom ratios are expected, and so are wider-angle arrangements.
To meet such demands, there are now various types of zoom lenses proposed in the art. Among prior zoom lenses having relatively high zoom ratios and compact format, there is a type comprising, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, a third lens group of positive refracting power and a fourth lens group of positive refracting power, as set forth in the following patent publications 1, 2 and 3.
[Patent Publication 1]
JP(A)2006-171055
[Patent Publication 2]
JP(A)11-52244
[Patent Publication 3]
JP(A)8-271788
Problems with the zoom lenses put forward in Patent Publications 1, 2 and 3 are, however, that as their total lens length gets short at increased zoom ratios, the effect of surface precision to aberration properties grows too large, resulting in difficulty with which lenses are processed, and an increase in lens fabrication costs.
Having being accomplished in view of such problems, the present invention has for its object to provide a zoom lens the total length of which is curtailed at increased zoom ratios, thereby reducing the ensuing effect of surface precision with good enough aberration properties, and an imaging apparatus incorporating the same.